Passengers who wanted to bring in plant material must declare it so it could be assessed for risk, he said.

"There are biosecurity signs located around the airport, quarantine inspectors on duty, and amnesty bins are clearly visible and are provided in the passenger arrival hall for the disposal of any last minute items. So not knowing is not an excuse."

The maximum penalty for knowingly attempting to possess unauthorised goods is five years' imprisonment and/or a fine of $100,000.

Passengers could ask MPI quarantine inspectors about any items they were unsure about, Keys said.